The lymphocyte transformation test for the diagnosis of Lyme borreliosis has currently not been shown to be clinically useful.

I would like to comment on the letter from Dessau et al.: “Lymphocyte transformation test for diagnosis of Lyme borreliosis is currently not documented to be clinically useful” [1]. I wish to thank Dessau and colleagues for their interest in our study and am very pleased that they confirm that the lymphocyte transformation test (LTT) shows a high specificity in seronegative cases [1]. Especially in such cases, the validity of the LTT is often controversially reported. As expected, the specificity was lower in seropositive samples than in seronegative cases, most likely due to the persistence of few, proliferating memory cells in the blood. Since antibody determinations often do not lead to secure diagnostic results, the specificity of 91.6% of the LTT in seropositive patients may be considered as acceptable. In many cases with positive antibody results, the suspicion of an active borreliosis can be eliminated by a negative LTT, although a false-positive rate of 8.4% must be considered in the assessment. Our publication points to the fact that clinical results are decisive for diagnosis, whereas laboratory diagnostics, including the LTT, may provide additional indications only. The diagnosis of borreliosis in 94 patients was based exclusively on clinical results, taking serology and medical history into account. In our manuscript, the clinical manifestations of 94 patients are described in the fourth paragraph, in the section “Subjects and Patients.” It is well known that borreliosis cannot be diagnosed unequivocally. The aim of the present study was to